Whipple Crater at the lunar North Pole: A smaller version of Shackleton at the lunar South Pole?

Whipple crater, approximately 25 km from the lunar north pole and on the far side of the Moon, is about 15 km in diameter and approximately 3 km deep. The floor and inner walls of the crater are not exposed to direct sunlight but are in some places illuminated by sunlight reflected from the rim. Located at ~130E Whipple is barely visible from Earth but the Lunar Orbiter Laser Altimeter (LOLA), an instrument on the Lunar Reconnaissance Orbiter, has provided the most detailed view yet of the crater and its interior, at a horizontal resolution ~10-20 meters. The rim is generally circular in plan view, has a maximum height above the surrounding terrain of about 0.5 km, although there is clear evidence of a loss of material into the crater interior in several places. The interior walls of the crater have an almost uniform slope of as much as 35 degrees indicating a conical shape to the crater not unlike that of Shackleton crater at the lunar south pole, which has with a similar slope. The floor of Whipple is irregular in shape, measuring approximately 5 x 4 km and has a relief of about 100-200 m and indications of a number of crater-like features as large as a few hundred meters in diameter. The LOLA data indicate that on 10 m baselines the slopes have an rms roughness of about 3-4 degrees, equivalent to less than 1 meter. These values are similar to those on the walls of Shackleton, a crater that is approximately 30% larger and deeper suggesting similar formation and degradation processes. Together, these data provide a characterization of these nearly permanently shadowed North and South polar craters that can be compared to the morphology and morphometry of non-polar craters of similar degradation states. This comparison will aid in detecting potential differences in crater interior processes in permanently shadowed craters.